Phonon anharmonicity of phonon band gap effect of scheelite PbWO ₄ studied by Raman spectrometry and first-principles calculations

The phonon-dispersions of PbWO₄ crystal are calculated using the first-principles calculations. Polarized Raman spectra in the PbWO₄ were measured in the temperature range from 4 K to 280 K, and the temperature dependence of the linewidth of the E_g (193 cm^-1) and A_g (906 cm^-1) Raman modes was analyzed using both the first-principles calculations and lattice perturbative approach. We found that the different behaviors of these two modes in the case of temperature broadening could be attributed to the large energy band gap in the PDOS (one-phonon density of states) resulting in different anharmonic interactions. The ratio of up-conversion TDOS (temperature-weighted two-phonon density of states) to down-conversion TDOS for E_g mode (193 cm^-1) is more than that for A_g (906 cm^-1). Therefore, the linewidths for the E_g mode (193 cm^-1) may be varied with increasing temperature by comparison with those of the A_g (906 cm^-1).